This report presents the findings of research undertaken by WRc, under contract to the Waste and
Resources Action Programme (WRAP). The research analysed the market potential for low grade composted materials in the UK, taking the risks associated with their use in different applications into account. It also assessed the viability of introducing standards for such products.
During the project, it became clear that differentiating between low and high grade feedstocks and
composts is a difficult task. The study has therefore considered all the major feedstock streams and markets based on the following philosophy:
- Any feedstock used for composting may contain hazards. This study does not exclude any
feedstock on the basis of quality or hazard content. The risk of unacceptable hazards varies between, and within, feedstocks.
The risk of hazard exposure is associated with the composting process and with product end use. This study mainly considers the hazards present in compost and the risks associated with its intended use. This is linked to the safe use of composts in different applications. Any hazards associated with the composting process are assumed to be controlled by applying a suitable regime licensed by the appropriate regulatory body.
The composting process may reduce (or increase) the hazards in feedstocks. The effectiveness of composting processes in reducing the hazards present in feedstocks varies.This study assumes that most hazards can be reduced if a suitable composting process and operating procedure is applied. Whilst many feedstocks can be composted to give a high quality product, those containing potentially toxic elements (PTEs), recalcitrant toxic organics or ‘contras’ (glass, metal and plastic residues) cannot because composting processes cannot eliminate these hazards. Contras can be removed through screening, but this has cost implications. The hazards associated with compost products will therefore vary according to those present in feedstocks and the potential of the production process.
Standards should be based on the quality of compost products. Standards should be based on a risk assessment of the hazards present in the compost in relation to its intended use. This risk assessment should be based on the source-pathway-receptor model. Lower quality compost products, subject to a less stringent standard, can consequently be used safely where the risks of hazard exposure are low.
Standards should be compatible with current and forthcoming regulations. This study takes the view that composting is currently “under-regulated” and further controls are required. Compost standards must be compatible with existing waste management regulations.
Current composting standard development is based on a high quality specification. Given the limitations of composting processes, significant quantities may be produced that will not meet the highest quality standards. Beneficial and safe use of lower quality compost would be possible through the application of less stringent standards that are appropriate for the designated end use. This study considers the application of less stringent standards for some compost products.
Approval of composting process and operation. The selection of feedstock and composting process should be by the operator, whilst the compost standard should define the limitations and permitted use of the compost. It is assumed that the compost operator will require a licence from the relevant regulatory body to undertake any particular process in a safe manner commensurate with any hazards. This licence will need to cover whether the process being operated gives sufficient attenuation of hazards to meet specified compost quality standards and how this should be monitored. This reflects the approach laid down by the Waste Management Licensing Regulations (WMLR), where a waste management licence is currently required for composting activities of more than 1000 m3/a.
3.1 Composting feedstocks
Current legislative trends mean that a wider variety of organic wastes may be composted in the future. This may include wastes with greater hazards which present increased risks to health, safety and the environment if not managed appropriately. The hazards might include toxic metals, harmful chemicals, pathogens, seeds, weeds and ‘contras’ such as glass, metal and plastic.
All feedstocks may contain hazards and could present a risk to health, safety or the environment - even greenwaste. There is therefore no distinct division between low and high grade feedstocks, particularly since quality may vary within a given feedstock. The composting process can reduce many hazards, with the exception of persistent chemicals (e.g. PTEs and recalcitrant organic compounds, including some pesticides).
‘Contras’ require pre and / or post treatment if they are to be removed by the composting process. Human and animal pathogens can be destroyed during composting, but feedstocks containing these can be perceived by stakeholders as undesirable. A subjective definition of low grade feedstocks could therefore be those that contain high concentrations of persistent chemical contaminants, contras or pathogens.
3.2 Composting process
Composting decomposes wastes into a stabilised organic material with more uniform chemical and physical characteristics than the feedstocks from which it was made. Composting can reduce many of the hazards associated with feedstocks, e.g.
i) sufficient exposure to temperature should attenuate most pathogens and weeds;
ii) the decomposing activity may degrade many, but not all, toxic organic chemicals;
iii) sufficient screening to remove unwanted glass, metal and plastics.
3.3 Composting Quality Assurance
The composting of hazardous feedstock materials will require more process control to ensure environmental safety and public confidence in the final product.
This will mean more Quality Assurance is carried out on composting sites. Some hazardous feedstocks will also only be composted by more advanced processes, such as in-vessel systems. Windrow composting is currently widely used, but may not be sufficiently controlled to ensure adequate destruction of pathogenic micro-organisms. Designing the composting process for a specified feedstock requires consideration of its associated hazards. A prime concern is the transmission of human, animal and plant diseases from feedstocks such as catering, animal and vegetable processing wastes. Greenwaste is also not without risks from pathogens.
3.4 Composting Markets and Applications
There are several large potential markets for the increased quantities of compost that might be produced in
response to changes stimulated by the Landfill Directive.
i) Horticulture – There is a substantial market in both commercial horticulture and home gardening for good quality composts to be used as plant growth media, soil improvers and mulch. Plant growth media need to meet a high standard in order to retain user confidence and a favourable public perception. This is the top end of the market where the most added value for compost will be achieved. Using compost as a soil improver may be particularly favourable because the technical specification for such products is less stringent. However, the potential for added value lies in the manufacture, bagging and retail sale of products. The cost of raw materials (peat and compost) is low. The current drive towards peat replacement should help market development, but the characteristics of compost means that it is not suitable as a direct peat replacement. Peat replacement represents a potential market for about 2 Mm3 per year (1 Mt/a) of compost by 2012.
ii) Agriculture – Whilst compost application to agricultural land for soil improvement and fertilisation is a potential application, there is strong competition in this market from farm produced organic wastes (especially manures). The Nitrates Directive means that restrictions on the application of nitrogen to land may limit this application. A derogation for compost might be possible, as the nitrogen it contains is stabilised (in slow-release form). Agricultural use is unlikely to be a lucrative market for compost, but may be enhanced if additional services (supply, incorporation, agronomic advice) are offered to the farmer. The quality of compost can be lower than for horticulture, especially if non food-chain crops are being grown. Establishing markets in this area would need to be supported by promoting the beneficial effects of compost as a soil conditioner and source of slowly released nutrients for crops.
iii) Forestry and Biomass Energy – There is a significant market for compost as a soil conditioner on land growing timber, including biomass and energy crops (e.g. poplar, willow). Compared with horticulture and agriculture this application would carry lower risk of public exposure to pathogens and fewer public perception problems and therefore lower quality compost would be acceptable.
iv) Land Restoration – Substantial quantities of compost could be used as an organic amendment to soils in land restoration, e.g. landfill completion, mine working restoration. The compost quality demands are similar to those for forestry and biomass energy.
v) Amenity land and green areas – Compost can be used as a soil improver on green areas between buildings, roads, park land and golf courses.
vi) Landfill – A potential application for large amounts of low quality compost is daily and intermediate landfill cover. The lowest quality compost (considered as stabilised biowaste) would be permitted in landfills. The benefits that composting offers to material used in landfill are significant reductions in waste volume and biodegradability.
vii) Incineration – Although not seen as a means of recycling organic waste, incineration may have a role as an outlet for stabilised biowaste.
3.5 Financial situation
Most of the applications described in the report are available for lower grade composts. However, these offer low added value because compost will compete with other cheap or no-cost alternatives. Achieving a sale price of £1-5 per tonne would be considered worthwhile and an addition to the gate fee revenue obtained for the waste feedstock. Composting of low grade feedstocks is likely to increase costs if their hazards are to be substantially reduced during the composting process. Economic and technical factors suggest that the production of high grade compost from low grade feedstocks will be minimal.
3.6 Likely scenario
Composting will expand and become a means of diverting biodegradable waste from landfills. The larger
waste management companies (particularly those operating landfills and managing municipal solid waste)
are likely to be key players. Such organisations will be able to operate composting facilities that are funded
by a gate fee. They will have sufficient in-house applications, such as daily landfill cover, land restoration
and landfill content. These will use lower quality compost, near to source, as part of the waste management operation. The compost will substitute for other materials, so they will benefit from cost savings.
3.7 The ‘Safe Compost Matrix’
Several potential compost applications could accommodate all the envisaged production. The risks posed from hazards in the compost vary from application to application. This means that compost standards should reflect the risks associated with the end use. Several sets of voluntary and legislative standards exist, or are being developed, to cover the use of compost in the horticultural market. A key concern here is the health, safety and environmental protection associated with using compost in this sensitive application. Products will need to comply with precautionary standards to retain stakeholder confidence.
Separate standards are needed for compost in other applications and these will have different degrees of risk associated with them. These should be based on risk assessment and could be developed from existing guidelines for the recycling of sewage sludge to agricultural land.
Environmental risks associated with compost application need to be controlled in a similar way to other materials in agriculture, forestry, land restoration and landfill operation. The application of sewage sludge to land is well regulated and standards are in place to ensure the safety of human health and the environment (e.g. as expressed by the “Safe Sludge Matrix” (ADAS et al 2001)). It is recommended that a “Safe Compost Matrix” be developed to give guidance on compost standards and the management for various applications.
The “Safe Compost Matrix” is intended to provide a practical and effective tool to help promote the expansion of composting in accordance with waste management targets. The “Safe Compost Matrix” (Table 1) therefore consists of:
- A high quality (multi-purpose) grade A compost suitable for horticulture (and other applications). This is essential to ensure environmental safety and maintain stakeholder confidence.
- A lower (general-purpose) grade B compost for use in less sensitive applications such as agriculture, forestry and land restoration. This would be in line with standards and regulations used to control application of sewage sludge biosolids to agricultural land, for example.
- A (stabilised biowaste) grade C compost, unable to meet either standard above, could be used for landfill cover, landfill or incineration.
The “Safe Compost Matrix” would incorporate caveats where a particular application requires higher quality
compost in order to present minimal risk.
This study, whilst recommending a “Safe Compost Matrix”, does not have the scope to develop a multifunctional Matrix of limit values. This is really the prerogative of policy-makers. The wider stakeholder community should be invited to participate in this process so that the limits have widespread support. This will help promote the production and use of compost.